Sam Michael admits McLaren's relationship with Mercedes will most likely not be "as productive" next season as the duo are set to split.
McLaren first teamed up with Mercedes back in 1995, winning three Drivers' Championship titles and one Constructors' crown.
The long-term partnership, though, is set to dissolve at the end of next season as McLaren have signed a new deal with Honda.
"There's no doubt that when you finish a relationship, whether it's with an engine partner or with anyone else, that part of the relationship is not as productive as the start of it, or probably the middle," Michael told Autosport.
"But it's been a very long one. Mercedes knows us very well and we know the people there.
"Obviously it wasn't a huge surprise for Mercedes because we are close to them. They've been aware that this possibility could eventuate."
The sporting director also ruled out the chance of Honda getting a McLaren chassis in order to test their engine, saying that would be against the regulations.
"The testing regulations cover last year's and next year's car, so McLaren as a team could not give them a 2014 chassis for them to run with," he said.
"We couldn't give them the 2013 chassis either to run in 2014. That's in the sporting code."